Repeating one digit of a 4-digit PIN can mean the difference between a phone that's safe and a phone that can be unlocked at a glance.

While a PIN limited to 4 unique numbers only has 24 possibilities, a PIN with three uniques and one repeated number has 36—which means those fingerprint smudges of yours won't betray you so easily. Just be sure the PIN you do end up with isn't one of the most commonly used PINs, like 1998. Photo via Ars Technica.